Rinse added fabric softener compositions are known. Typically such compositions contain a water insoluble quaternary ammonium fabric softening agent dispersed in water at a level of softening agent up to 7% by weight in which case the compositions are considered dilute, or at levels from 7% to 50% in which case the compositions are considered concentrates. In addition to softening fabric softening compositions desirably have other benefits. One is the ability to confer soil release properties to fabrics, particularly those woven from polyester fibers.
One of the problems associated with fabric softening compositions is the physical instability of such compositions when stored. This problem is accentuated by having a concentrated composition and by storage at either low or high temperatures.
Concentrates and storage stability at extreme low or high temperatures are however desired by the consumer. Physical instability manifests as a thickening on storage of the composition to a level where the composition is no longer pourable and can even lead to the formation of an irreversible gelation of the composition. The thickening is very undesirable since the composition can no longer be conveniently used.
In the past physical stability of rinse added fabric softener compositions has been improved by the addition of viscosity control agents or anti-gelling agents. For example in EP 13,780 (Procter and Gamble) viscosity control agents are added to certain concentrated compositions. The agents may include C.sub.10 -C.sub.18 fatty alcohols. More recently in EP 280,550 (Unilever) it has been proposed to improve the physical stability of diluted compositions comprising biodegradable, ester-linked quaternary ammonium compounds and fatty acid by the addition of nonionic surfactants.
With concentrated compositions comprising biodegradable ester-linked quaternary ammonium compounds the problem of physical instability is more acute than with traditional quaternary ammonium compounds.
In EP 0,040,562 (Lesieur Cotelie) a nonionic emulsifier/stabilizer is added to a concentrate comprising an ester-linked quaternary ammonium compound to form a viscous gel. The stabilizer is a C.sub.12 to C.sub.14 alcohol ethoxylated with 9 molecules of ethylene oxide. The degree of branching of the alcohol is not, however, mentioned.
Certain nonionic stabilizing agents not only stabilize concentrated compositions comprising biodegradable quaternary ammonium compounds but are also environmentally friendly, in that they show acceptable biodegradability and are not substantially toxic in aquatic systems.
Soil release properties are generally imparted to fabrics by the use of separate soil-release agents, usually a high molecular weight polymer, in a detergent composition or separate treatment. For example in EP 0,398,133A (Procter & Gamble) there is disclosed a cationic polymeric soil release agent for use in a fabric conditioning composition.
A disadvantage of such compositions is that the soil release agent increases the number of components in the formulation, increasing cost and making the product less environmentally acceptable.
We have now found that fabric softening compositions comprising biodegradable ester-linked quaternary ammonium compounds confer improved soil release properties to fabrics.
We have also found that temperature stability of compositions containing biodegradable quaternary ammonium compounds is improved by the use of selected nonionic stabilizing agents.